1. Field of the Inventions
The present invention relates to signal processing apparatus for use with image sensing apparatus or the like, and more particularly to signal processing apparatus for processing analog and digital signals.
2. Description of the Related Art
Various methods for processing an output signal of an image sensing device such as a CCD are known.
For example, many methods of converting an output signal of an image sensing device into a digital signal by means of a high-speed analog/digital converter (hereinafter referred to as an AD converter) and then subjecting the resultant signal to digital signal processing have been proposed. More specifically, this type method is arranged to effect AD conversion of a sensed color image signal, to execute signal processing required for an image sensing device, such as filtering, gamma conversion, matrix conversion and clipping, in a digital manner, and further to effect DA conversion by high-speed digital/analog converter (hereinafter referred to as a DA converter) for producing a video signal.
In known image sensing devices using such digital signal processing, the circuits which were used in an analog form were simply replaced with corresponding circuits in a digital form. There have been accompanying problems such as device size or production cost cannot be reduced, as a result of a larger circuit scale, an increased number of parts, and a greater consumption of current.
Also, because digital circuits and analog circuits exist in a mixed relation, interference due to mixing of digital signals with analog signals presents an obstacle in obtaining a desired SN ratio or reduction of circuit size.